Microbiology Chapter 3: The Cell

Microbiology - Chapter 3: The Cell

• Microorganisms vary greatly in size and shape, visually observable microscopically. They also differ in metabolic capabilities.
• Francesco Redi's experiments disproved spontaneous generation for maggots, showing flies were the source.
• John Needham supported spontaneous generation of microbes in broth.
• Lazzaro Spallanzani's experiments challenged Needham's findings, suggesting microbes in the air caused contamination.
• Louis Pasteur conclusively disproved spontaneous generation with swan-neck flasks. He proposed "life only comes from life."
• Robert Hooke first described cells using cork observations, published in Micrographia.
• Rudolf Virchow popularized the cell theory in "Cellular Pathology" (1855), arguing that all cells arise from pre-existing cells.
• Robert Remak's work from 1852 supported the cell origination from other cells.

Endosymbiotic Theory

• Mitochondria and chloroplasts evolved from bacteria.
• These bacteria formed a symbiotic relationship with host cells.
• This relationship led to the evolution of mitochondria and chloroplasts.

Importance of Handwashing

• Ignaz Semmelweis championed handwashing to prevent disease transmission among physicians in the 19th century.

Germ Theory of Disease

• Joseph Lister used antiseptic procedures in surgery, contributing to germ theory acceptance.
• Robert Koch developed a protocol for determining the causes of infectious disease, supporting the germ theory.

Prokaryotic Cell Structure

• Prokaryotic cells lack a nucleus and membrane-bound organelles.
• Their DNA is in a nucleoid region.
• They contain ribosomes (70S).
• Some prokaryotes have a cell wall, maintaining morphology and resisting osmotic changes.
• Possible inclusions to store nutrients.
• Some form endospores to survive harsh conditions.

Prokaryotic Cell Shapes and Arrangements

• Prokaryotes have varied shapes (coccus, bacillus, vibrio, spirillum, spirochete).
• Cells can be arranged in single units, pairs (diplo-), clusters (staphylo-), chains (strepto-), and more.

Prokaryotic Cell Membranes

• Bacterial plasma membrane is a phospholipid bilayer with proteins embedded.
• Some molecules move passively via diffusion. Active transport for larger molecules is common.
• Archaeal membranes are distinct, with ether-linked lipids.

Prokaryotic Cell Envelope

• Cell envelope includes the plasma membrane and a cell wall (typically peptidoglycan in bacteria or pseudopeptidoglycan in archaea).

• Differences exist between gram-positive and gram-negative bacteria, related to the cell wall structure.

• Some bacteria produce glycocalyx coatings like capsules and slime layers aiding in attachment and avoiding the immune response.

Prokaryotic Appendages

• Pili/fimbriae aid in attachments and gene transfer.
• Flagella (including different arrangements) propel movement in water.
• Bacteria use "run-tumble" movements for directed movement.

Eukaryotic Cell Structure

• Eukaryotic cells have a nucleus containing DNA.
• Cytoskeleton provides structural support and transport.
• Components include microfilaments, intermediate filaments, and microtubules.
• Centrosomes are microtubule-organizing centers.
• Mitochondria are complex, double-membraned organelles with cristae for cellular respiration.
• Chloroplasts have thylakoid membranes for photosynthesis.
• Endomembrane system is a series of interconnected membranes (rough ER, smooth ER, Golgi apparatus, peroxisomes) for modifying and transporting materials.
• Ribosomes (80S) are significant for protein synthesis.

Eukaryotic Cell Shapes

• Eukayotic cells can come in numerous shapes and structures, reflecting diversity and specific functions.
• The presence of organelles and other cellular components distinguishes eukaryotic cells from prokaryotic cells.

Eukaryotic Cell Membranes

• Eukaryotic plasma membrane is lipid bilayer with embedded and integrated proteins.
• Contains sterols (like cholesterol) for fluidity maintenance.
• Glycoproteins/glycolipids for recognition and communication.

Transport Across Membranes

• Prokaryotic and eukaryotic cells have varied mechanisms for materials' movement across membranes
• Active and passive transport play roles in movement and maintenance within these cells.
• Endocytosis and exocytosis allow for taking in and releasing large materials into the cell.

Eukaryotic Cell Walls

• Eukaryotic cell walls differ and provide structural support to cells.
• Cell walls are not present in all eukaryotes.

Endospores

• Endospores are features unique to some prokaryote cells.
• The ability to form endospores enables cells to withstand harsh conditions.